Like the liberty taken with the Prince '90' and '110' and the early Black Ace having '98' on it, the Wimbledon 88 and 98 made reference to the series rather than an absolute measurement of the head size, I reckon.
We sold a ton of the HM series back in the late '80s. I played the Eclipse Expert 88 in '91 or so...great racket.
I do wonder what the VEM 15 designation refers to. I'm not familiar with that model.
Easy for me to say; but, how about some pics ?