And these were all booked via BA, simple flight only tickets? (So not a BA Holidays booking, etc)

I had a LCY flight two weeks ago that posted based on eligible spend, so not sure why those would have posted differently to you.

Assuming this was a straight forward ticket (and you’ve done the sums to confirm eligible spend minus taxes and surcharges would net you more Avios), may be worth a call to BA to get it changed.