"It could be something as simple as a later calving date, a record of an AI sire when it was actually a stock bull son of the same bull, or a bit of preferential feeding for some animals before the assessor would be around gathering up data on the performance of progeny," he explains.
"Thankfully, there's less scope for that today, especially with genomics and DNA verification of pedigrees. That's going to eliminate both genuine mistakes and the less genuine ones and I'm really looking forward to seeing the results of these developments over the next five years."
Despite his misgivings about the veracity of all the data available on bulls, Whelan's favourite bed-time reading at the moment is his Bull Tracker Report from ICBF.
"See this?" he says, shoving the booklet over the table to me. "That is the best thing ever. It shows how all of the bulls that I ever sold out of the place over the last decade actually performed on each farm."
I sit there absorbing the liveweight gain figures for the progeny of Whelan's bulls from all over the country.
"It's the first time that a breeder gets a chance to see if the choices that he is making are delivering results at farm level," declares Whelan.
"But, but," he quickly adds, waving his finger. "There were mistakes in it. There was a slight mistake with those weight gain figures and I pointed it out to ICBF. And, in fairness, they listened and recalculated the figures, and sent me a new version and all."
BACK TO THE FUTURE
When I ask Whelan what bulls he is using on his herd this year, he looks sheepishly at Clive, his AI technician son. "We've a little bit of everything in there," Clive laughs.
"It's not like the dairy man who only wants the top five or 10 EBI bulls out this year. We'd be using straws of bulls that aren't being sold at all anymore.
"Some very popular ones like Altea, Brooklands, ERE and Vagabond. Bon Jovi, Nipper, Saphir and CF52 would also be used on the Charolais cows. But we'd also use test bulls on about 15pc of the herd every year," Clive explains.
"Only on the cows mind you. I don't care how high a score a test bull has – he's too big a risk on heifers," chips in Tom.
Despite this willingness to try new genetics, going back to use a bull that has proven his worth is something that Tom is keen on.
"I started using a Limousin bull called On-dit again this year, even though I first used him five years ago. I started hearing lads talking about him again last year, so I rang up a few of the farmers that had bought sons of his from me in 2009.
"One guy told me he'd only let me come and have a look if I promised not to try to buy the bull back. But I could see that he was doing the business.
"For me, seeing the animals on the ground is a big factor in my breeding decisions. There's only so far that you can get with figures that come out of a computer. You've got to use common sense too.
"And yet, you'll still get guys who will want to check docility ratings for a bull, even though they may have been handling their progeny in the yard no problem."
Tom Whelan is an avid reader of all the information ICBF collate and disseminate but he wonders if beef farmers are quite as clued in.
"I've a lot of time for all the data that ICBF generate but a lot of lads either don't realise the importance of reliability or are just too bamboozled with all the figures on every bull to take note of them," says Tom.
"I think there should be a colour code system based on traffic lights for reliability. Say green for any bull with over 70pc reliability, orange for 40-70pc and red for any bull with under 40pc. That would immediately send the right message to farmers when they are choosing bulls."
One of the most striking statistics from this Wexford farmer's set-up is his claim that he has lost only one calf in the last three years.
"And that one was because some lads were out lamping in the field and startled the cow during what was already a difficult calving," recalls Tom.
So what's the secret?
"The first thing is to have your heifers calving at 2.5 years old. I know the scientists might say that we should be aiming for calving at two years but my experience is that an animal often is not developed enough before this which can lead to all kinds of calving difficulties. I am also convinced that an animal that calves before she is fully grown never catches up with her comrades.
"The other thing that I would be very particular about is only ever using easy calving bulls on heifers. Epson, Altea and On-dit on the Limousin heifers and Nipper and Pirate on the Charolais.
"I'd also be very strict about the diet of all in-calf animals. I do the same as they do in France and what our fathers used to do – two scoops of oats daily before they calve."
How much is in a scoop, I ask.
"I've no idea, but I know it works," he laughs, adding that he will often feed 2kg of soya to the bad milkers for a few days before they calve to increase their milk yield.
"When the cow does actually calve, the first thing we do after turning her out of the pen for safety is get 2.5cc of a selenium injection called Vitesel into them. I believe the whole east coast is deficient in this mineral and the shot costs me about 50c per calf.
"I also give a vitamin B12 intramuscular injection to each calf. Since I started this, I haven't seen so much as one scour and the calves are all up and sucking very fast. That is costing me another 30c/calf.
"I also spray a little iodine just behind the cow's shoulder after she calves so that if she wants to get a lick of iodine, she can lick herself rather than licking the calf's navel. All the cows also get an Allsure mineral bolus around St Patrick's Day."
Never afraid to buck convention, Whelan also tried out an idea he came across in France some years ago to prevent ringworm infestation.
"It's just a branch of holly in every shed, and I can't tell you how it works, but it just does," he says.