It is a strip fuse, not necessarily a fast-acting device. Look at any one that has been in service and it will show the signs of heating by its droopy profile.

Remember, it started and peaked at 99, but started to drop fast. It was down below 80 before too long.

A fuse is rated by its I^2 *t profile, i.e. some element of the current flow and the time it is subjected. The fuse should be permanently capable of passing 80A through. Pass 81A and at some very long time it may open. Pass 90 through, and it would be a bit shorter time. Pass 100 and even shorter... Pass 1000A and it would pop. Short circuit it and it would pop.

In the big scheme of things 99A for a few seconds and dropping fast isnt far from 80A. Breakers and fuses have to be able to support some overage for a short while in order to allow for inrush currents during motor starts, fault isolation and clearance, etc.m depending upon the system. The glow system is definitely very simple, but it still must do 80A continuous and thus 99A for a spurt is no big deal.

Other systems can be far more sensitive, and the protection devices can be designed accordingly.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)