I don't think Lucas ever did change their rating. The wikipedia article at
https://en.wikipedia.org/wiki/Fuse_(automotive) seems to have the correct information.
Confusion stems from the various same size package but different inside versions made to other specifications such as AG et al. This page from Littlefuse
Glass Fuses | Automotive Glass Fuses - Littelfuse gives some idea of the variety in glass tube types. Several are made to same size as the automotive fuses but the ratings are as per specific specifications. That page looks to be anything but comprehensive.
Lucas ratings are quite conservative. Half as much again current as the rated one is almost invariably safe. Unlike UK mains in-plug fuses there is no great concern over protecting the wiring harness as, for nearly all loads, wires are well oversize.
Realistically if it has the correct colour code card inside it should be to Lucas specs. If it doesn't have a card its anybodies guess what's actually inside. Something as, apparently, simple as wire tension affects the relationship between actual instant blow and continuous blow currents.
Clive