Across all the variants, MOF177e versions with soft start and electronic variable speed have some differences from the MOF177 fixed speed routers. The armatures are longer to take a disc on the top end of the armature (contains a magnet and works with a hall effect sensor so that the electronics can sense and control the spindle speed). There are electronics up top and a longer top cap to house them.
Type 1 and Type 2 both have the dark grey / light grey plastic mouldings and orange coloured power switch and speed control dial.
Type 2 has a push button spindle lock that may not have been there on the type 1.
I think that type 3 changed the colour to all dark grey instead of two tone and orange controls changed to blue. I think that's when manufacture moved from Switzerland to Italy.
Type 4 I'm not sure but I associate it with Elu's takeover by dewalt. Under the dewalt control they continued to manufacture in Italy in the dark grey plus blue controls colour scheme for a short while before rebranding the machine as a Dewalt DW625 in the current black and yellow colours.
These are the superficial changes that may help you recognise the machines. There were some small real changes as well but not very obvious. If you hunt, you can find exploded parts drawings for most of the variants and try to figure it out.
In my opinion, if you have a type 2 you got one of the best - I believe they were all made in Switzerland and I think they are better than any of the later Italian manufactured units and the Dewalts.
Overall, the machines haven't changed a lot over the years so there's a half decent chance that a dust hood for a type 4 would fit a type 2. The exploded diagrams may help you figure it out.
I have a type 2 and if you set it to minimum speed and switch it on, it spins up without a kick and sits there purring. Reminds me of that advert where someone balances a coin on edge on a sports car engine. Lovely smooth machines.