Hi jcjeant,
I think you'll find that in 1988 many airliners (particularly American ones) were still using scratch-foil (analogue) flight recorders, monitoring about 7 parameters. The DFDR on the A320 was advanced for its time.
BTW, it was unfortunate that the QAR cassette in the electronics bay was (presumably) destroyed in the ensuing fire, because that would have revealed even more data than the DFDR.
***
PS [by EDIT on Jan24]
Now that DozyW has provided that useful link to the relevant FARs
for the present day, it may be worth having a look at the FAA regulations pertaining, at the time of Habsheim (1988), to turbine-powered airplane types that had been
type-certificated before October 1969.
14 CFR 121.343 - Flight data recorders. | LII / Legal Information Institute
Types still enjoying the leniency of the above FARs in 1988 would have included all derivative models of B737 and DC-9 (and presumably the MD-80 series, which was certificated by amendment to the DC-9 type-certificate).
To summarise the relevant parts:
aircraft in that category (type-certificated before Oct 1969) needed only 6 parameters (one of which was time), although by 25MAY1989 the 6 parameters had to be recorded digitally (so the scratch-foil recorder was no longer acceptable), and by 25MAY1995 the minimum number of parameters rose to 11;
and individual aircraft manufactured after 26MAY1989 needed a DFDR with a minimum of 17 parameters.
So in the case of a B737-400, which was competing for sales head-on with the A320, I infer that hulls manufactured at the time of the Habsheim accident could have been registered in the U.S. with a 6-parameter DFDR, or even a scratch-foil recorder initially.
*** [by EDIT on Jan27]
Re the A320 QAR, further enquiry suggests that - on the contrary - it only records roughly the same number of parameters (and the same sampling rates) as the DFDR, although the precise specification may vary from airline to airline. A print-out of a 1988 BCAL/BA A320 QAR confirms this, and is presented in 5 "passes" - roughly corresponding to the 5 "tomes" shown in the BEA report for Habsheim.