That's great if you have an encyclopedic knowledge of old posts and old topics, as someone who uses Victoria semi regularly I've never seen one sat in Victoria, but as you mention short notice diversions and route knowledge training from the Gillingham depot it seems when I took a look at RTT makes sense.
I just also remembered that while routes were being transferred from Southern to Thameslink there were transitional stages where the stock had to be used into Victoria. I think it might have been back in 2016 they were first cleared? My post wasn’t meant to be criticism, just pointing out that it had been going on quite a while.
The public version of the sectional appendix I have, (downloaded in 2018), had them cleared for all the platforms at Victoria. There are separate entries in the table for the two sides; Kent 1-8, and Sussex 9-19...
