Mod version check reports base 1.1.62
despite the fact that Factorio is only 1.1.61
is this intended or did something get missed when the mod was updated?

No, it is correct. 1.1.62 is still ‘experimental’ so you have to opt-in to the experimental branch on steam, or enable experimental updates in the game settings if not on steam.

You can check the homepage (https://factorio.com/) for info on which version the latest stable and experimental are.

All the changelogs are on the forums (https://forums.factorio.com/viewforum.php?f=3) and Filter Chests uses the feature added in 1.1.62:

Added support for container entities with filters by using inventory_type = "with_bar" or "with_filters_and_bar".

thanks, I just wasn't sure.
still on the standard branch, as it's got fewer bugs.

1.1.68 is now stable so Filter Chests can be installed by stable-branch players :)