I've done a few marches enough to see the force for good are way out with their figures .
Secondly I've never seen them count marches and believe me I checked that with the Glasgow march in January.

I've seen pittodrie with 15.000 fans in the stadium when fans start leaving with 10 mins to go which will leave 11000 and the disperse after 5 mins .

That Glasgow march was the biggest yet by miles.

Force for good even suggested the marches were going past the end and doubling back again to make the numbers appear much more.
After that I stopped taking their 30-50 UJ flag savers seriously.

But the lad that organises it is a very nice lad .
After the Aberdeen independence march I saw him cross the road to the train station I said to him I admire his passion and shook his hand he replied to me and said the same.
Seemed an all round good guy.

I kindly refer you to the below link which includes a video of the whole march as well as a description of the counting methodology.

https://www.aforceforgood.uk/single-post/2020/01/11/Unionists-Stand-Up-to-SNP-Glasgow-March

I've been on plenty marches too, albeit a completely different type, and you don't get much of an idea of the scale when you're in it yourself.

Good to hear you like Alistair!  He's a nice guy.