No they're not. They never give a figure. They sometimes claim 'more than last year' or over an arbitrary amount but they never communicate how many season tickets have been sold.
They do, announce it annually https://www.barnsleychronicle.com/article/28436/reds-sell-7833-early-bird-season-tickets
Chronicle announced it, not the club. And even the chronicle quoting flatman doesn't give the figure. So the chronicle must have found out one way or another.
It's only on the odd occasion they state the numbers during sales, it usually then comes out in club forums and Q&As later in the season.
Its obvious it's come from a club source, pretty sure Khaled released some figures during his time. Matters not to me either way, I guess we'll find out in due course next season from attendances.