Before I get started, it is important to note that this post is speculation and I openly own it as such.
Some time ago, this document was posted on the board: http://www.dtic.mil/dtic/tr/fulltext/u2/a135274.pdf
This document, written in 1983, chronicles the then current siren offerings (both electronic and mechanical) in that era. Rare gems such as the Whelen 2000-R, Alertronic 5000, and EOWS-812 are noted as then-offerings from their respective manufacturers. At the time, one article of confusion that was brought up was the Whelen WS-2500, an omnidirectional siren listed at 115 dB. At the time the document was posted, there was speculation the WS-2500 was another name from the WS-2000-16 or WS-2000-20. The former seemed likely based on the output (and the fact it was missing from this document and was known to be around); it seemed the 2000-20 didn't materialize until later in the 80s based on extant advertising literature. The 2x00 nomenclature always seemed to denote fully omnidirectional designs that were not speakers pointed in the cardinal directions.
So this is where my theory comes into play. In a moment of boredom earlier, I was reviewing patents and of course I came back across the patent for the WS-3000 speakerhead as granted to Bruce Howze (submitted 1981/granted 1982): https://patents.google.com/patent/US4344504A/
The thing is, that patent also covers a truly omnidirectional speakerhead using 100W drivers (Figs. 7-9). The design and means for directing the sound clearly predate the design Howze would invent for the 2700 series. That head has never been seen in the wild. But wouldn't the design + the naming scheme make you think that could be the 2500? We know these designs may never come to fruition (ex. the 2001 patent containing a revision of the Thunderbeam using the 2001 head). But this head was designed for Whelen (obviously since Whelen is listed as an assignee of the patent), so it was meant for outdoor warning. Also, the design looks inefficient and leaves the drivers open to the elements. Not to say the final design, if it was ever put out, was exactly like was in the patents, but its surely not a design that would have lasted. And, as I've already implied, the design was clearly reworked to become the 2700 series.
Anyway just something that came to mind. I'd love any thoughts y'all have.