Cambridge to Maidstone Stations

I wish to be able to travel from Cambridge to Maidstone as a day return trip, leaving before 0830. My preferred route is via St Pancras and Strood to Maidstone West. However I want the option on the day of going via Victoria to Maidstone East or returning that way (for example if there are cancellations, or I fancy a change).

The ticket I bought is an Anytime Day Return "valid via any permitted route" for £61.60. There is also an Anytime Day Return "not valid on HS1" for £58.30 which I didn't buy.

I notice however that there is no + symbol denoting validity on the London Underground. Can I assume therefore the ticket is NOT valid for travel via Victoria? What if I used oyster to get between St Pancras and Victoria, would my Day Return ticket be accepted on the Victoria to Maidstone segment?

The Cambridge to Maidstone ticket you have bought should have the '+' symbol. Where did you buy it from ?

It should have a Maltese Cross. Are you sure?

I bought it from Cambridge Station and there's definitely no cross:

Oh dear, that's supposed to be a cross isn't it. I can't see it with my eyes, it looks like an up arrow.

Yes. Depending where you obtain such tickets they will show the plus symbol, the 'dagger' (as on yours) or an actual Maltese Cross. I agree that the dagger is the most difficult to identify at first sight.