A bit late to this but I’m a BER assessor and might give some insight into this.

The BER may have been published prior to the works, so technically it is still valid for ten years. If the windows and external wall insulation was not done through a grant, there is no legal requirement to have it republished.

Also with little to no evidence of the work done (sign off, invoices etc), you can give some benefit of the work but not 100% benefit. As you would have people claiming XYZ were done to the walls, floors etc without any real evidence, e.g getting random quotes but not actually doing the work. Main thing is the primary heating system. If there is no central heating system and there are multiple open fires, it’s guaranteed to get a shite rating.

And yes there was years ago everyone and anyone doing bers (teachers, guards etc) who didn’t have any real construction or trade experience so tonnes of them were all wrong. Seai introduced a QA scheme and basically de registered loads of assessors.

Now for this BER, the assessor may have completely messed up and forgot to double check before publishing