Is there any way to know when NOT to use my Oyster card?

I have been living in London for many years yet I still can't figure out when I am not allowed to use my Oyster card and I have to ask every time I suspect that it can't be used.

Two recent examples:

Trains from Paddington to Slough for example stop at Ealing Broadway, Southall, Hayes & Harlington, West Drayton and Langley

I know for sure that I can use my Oyster to go to Ealing Broadway as I have done it hundreds of times and I am very sure that I cant use it to go to Slough. I cant remember which of the rest of stations are within the coverage of the Oyster card. There are no signs at the station to explain that.

Trains from St Pancras to Ebbsfleet

If I remember correctly I can get off at Stratford, no problem using the Oyster card but you have to buy a ticket if you are going to Ebbsfleet

Again no signs and no way to tell not even the ticket machine warns you about that.

Is there something I am not aware of?

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Is there any way to know when NOT to use my Oyster card? - From below of diverse lost travelers with backpacks exploring woodland and searching way in cellphone

Is there any way to know when NOT to use my Oyster card? - Passenger using credit card for paying taxi ride

Is there any way to know when NOT to use my Oyster card? - Woman Sitting on a Couch Using a Laptop and Holding a Credit Card

How do I know if my Oyster card still works?

If you have an Oyster to pay as you go card, it does not have an expiry date. The credit will sit on your card until you are ready to use it again. However, if you do not use for two years it will stop working, even if you still have money on it to pay as you go.

Do Oyster cards go out of date?

Unused credit on your Visitor Oyster cardThe pay as you go credit on your Visitor Oyster card never expires so you can keep your card until your next visit, or lend it to family and friends. If you don't need your Visitor Oyster card, you can get the remaining credit refunded.

How long can an Oyster card be inactive?

There is no expiry date on Oyster cards. Dormant card? Oyster cards unused for 12 months or more. Dormant fees?

Do Oyster cards deactivate?

We can then transfer your remaining pay as you go credit, Travelcard or Bus & Tram Pass to your new Oyster card. You must have pay as you go credit, or at least five days travel remaining on your Travelcard or Bus & Tram Pass, for us to transfer it. Your card will only be stopped once you've reported that it's lost.

Oyster Card VS Contactless - EXPLAINED

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: Andrea Piacquadio, Kamaji Ogino, Tim Samuel, Karolina Grabowska