Not 100% sure about this, guys. Let me explain.

Chris Thrale in his book gives the serials of Vulcans sold by Pax as starting at 558450 in August 1979, rising to 674758 by July 1980 and 904338 in November 1980. Which seems like one serial range.

But he also identifies an early (no further detail) Vulcan with a 900000 range serial, and a Mk2 with serial 019006. And the OP's is 026461.

And stop and think about it.

Chris' data from Pax suggests that if the Vulcans were numbered serially, one at a time, that Webley made about 200,000 Vulcans in a ten-month period and then more than 200,000 in the next five months. 600-1200 a day, if my mental arithmetic is right. If there are, as estimated, 4 million air guns in the UK, then about half of them should be Webley Vulcans.....

Troubledshooter: it can't be 1975. The Vulcan was introduced in 1979.

As for the Tracker/Viscount, yes, they appear to have been numbered together, and in a different sequence from the Vulcan. But the Wallis 2006 sale included Trackers numbered 4192, 10012, and 1512. Rifle 4192 was a Camo Tracker, a model introduced in 1986.

It's all a bit confusing.