Especially since TCP is often introduced like "TCP provides reliable, ordered, and error-checked delivery of a stream of octets (bytes) between applications running on hosts communicating via an IP network" or similar formulations (this one comes from Wikipedia). "Reliable" does seem to imply that all data sent is also received. It's of course impossible to guarantee that.

Actually I think it's even a mistake to call TCP reliable. It's best-effort, and allows you to detect disconnects. That's all it does because that's all it can do.