If the older 6SN7GT spec is safe in an amp, then it is ALWAYS safe to use 6SN7GTA or 6SN7GTB in those same slots. The later GTA and GTB versions of 6SN7 are exactly the same as GT, but with higher ratings for plate voltage and dissipation (this means they’re more robust). The REVERSE is not always true. If an amp calls specifically for 6SN7GTA/GTB, you might be straining old GT tubes by running them in that slot - just depends on the amp. Quite honestly they’ll still probably work fine, but will wear out quicker. Note that for audio purposes, GTA and GTB are exactly the same. Also the GTA & GTB versions typically have less issues with noise & microphony than old tubes GT. On the flip side, the old GT tubes are usually known to sound "sweeter". In a preamp or phono stage, the old 1940s GT tubes are usually going to be too noisy, but in a power amp they’re fine (and IMO that's where 6SN7 belong!).
The modern Russian Tung-Sol 6SN7 is a GTB, which is handy in amps that call for GTA/GTB. In some amps (like my VACs) it’s popular to call for GTA/GTB in the driver (V2) slots, and run them at higher voltages than in V1. In my VACs I like running old GT’s in V1 but stick to the called for GTA/GTB in V2 (the modern Russian tubes are actually FATASTIC in this role).
Subs like the ECC33 must be done more cautiously, because the extra heater current draw is significant. However, if the manufacturer says OK, it should be fine. It’s an extra strain on the transformer in the PSU, but it that’s safely within limits (you basically add up the current draw amperage from all tubes and check if the transformer is rated to supply that), it will NOT affect the downstream tubes other than contributing its own unique sonics.
Also watch out for 5692, which some people like to sub for 6SN7 (red base RCA and GE being popular). This tube has much lower plate ratings than even 6SN7GT. If you put this tube in a GTA/GTB slot it can be bad news! This tube is famed for its purported "10,000 hour life" but it won’t last for long if run way beyond its ratings! They ARE very mechanically rugged, though!