My Boat (since sold )was Hull number 63 with a build date of December 2007.
I was the third owner at the time and neither of the two previous owners had been Members of the Association, in fact the "join the PSSA" leaflet was still with the Owners manual and other paperwork handed over to me. This would suggest that in probably a good few cases it was second owners onwards who joined in the later years. I discovered the Association when researching the purchase of a 235 for example.
However that gives us a definitive "end number" for 2007 production of the 235, leaving no's 64 - 70 to cover 08 onwards. I would guess the majority of those were built in 2008 as Public information from Companies House shows that the initial filing for the Voluntary Liquidation of Parker Lift Keel Yachts was made in July 2009.
Of course Bruce Parker under the BP Sailboats guise continued to offer the 235 for a while afterwards along with various spares but I'm not sure whether he actually built any new 235 Hulls. Of course BP Sailboats is no longer trading.
It doesn't seem like a definitive list of build dates will emerge to answer the OP's question.
The proof of Vat paid rules on selling / buying might prove to be a help here. Maybe existing owners could add their build dates if they know them to help construct at least a partial list with (hopefully)not too many gaps.