Winds of Chaos

I've found 3 separate 1e fan-adventures which take place in or near the city of Almarr.
Where is Almarr supposed to be and why does it appear in old Warhammer adventures?

I haven’t heard of it (not very helpful, I appreciate.)

I suspect it might be a something created for someone’s own personal game, unless someone else has more information. What are the fan adventures it appears in? Are they by the same person?

That's what I thought at first, but it's talked about like the audience should know where it is. They're all by the same guy, so it's likely his world, but I thought that world might be published elsewhere. The adventures don't say "The players are in a town called Almarr", which is standard fare for such things. Instead it's "The adventures are in Regalia, which is 60 miles west of Almarr." Or "The adventures are traveling between Almarr and Middelton" rather than "The adventurers are traveling", so it's clearly expected that the audience should know what they're talking about.

The adventures are: Wild Horses, Vermin Tide and The Butterfly of Bagus

Could they be alternative names for the Reikland, Altdorf, and Middenheim? I wonder if the author was being cautious about using official names.

From the place names, it sounds like the author may have been using a pre-WFRP1 conception of the Old World, when things were a bit less clearly defined. Middleton in particular is similar to the sorts of place names used in the WFB2 supplement Blood on the Streets: set in 'The Riding' with settlements called Averridge, Stoodthorpe and Mayby. In any case I would take Almarr and the others as definitely not canonical places.

This sounds about right that the author made up these places. Using non-canon places would give the author a greater freedom in what is there and not and what can happen.