How is it the 25th anniversary when Highly Responsive to Prayers came out in 1997?

Pgj1997 said:

How is it the 25th anniversary when Highly Responsive to Prayers came out in 1997?

TouhouWiki says:

The Highly Responsive to Prayers was apparently finished in 1995 (while ZUN was still attending college), which is why he tends to mention that year as the start of the series.

Tapper said:

Highly Responsive to Prayers was apparently finished in 1995 (while ZUN was still attending college), which is why he tends to mention that year as the start of the series.

No disrespect to ZUN, but... that's not how anniversaries work.

Pgj1997 said:

No disrespect to ZUN, but... that's not how anniversaries work.

For what it's worth, they also mentioned HRtP was shown to the public a year earlier, in 1996.
Besides, given that it started out as a study project, I can understand why he thinks when he finished it is more important than when he published it.