I’ve checked every platform like 10 times and only found: 22/25 maps 24/25 hydrants 21/25 hats 24/25 cannons Are there any really well hidden ones, at depots I’ve got the hats at dawlish on the bridge and downstairs at Plymouth.
There some in Laira and exter depots and at Dawlish walk along the see wall and there some there and further down on a foot bridge.
But what are the collectible, on any route, they are never listed as such, just some wied picture in the menu and no legend as to what they are
Watch the route introduction (accessed via tutorials when selecting the route, same place you access timetable and scenarios) and it'll tell you what you need to find. On Riviera, there are four (25 of each): route maps, cannons, hard hats and fire extinguishers.
Video you are not seeing everything unfortunately, as everything are going too fast a true guide is a written document, videos are good to show a quick over sight of somewhere or an event that happened
