Abbreviations can help you understand a text without telling you how to address the person who wrote it. In dating, separate recognising a term from deciding that it belongs on someone else's profile or in your introduction of them.
Decode the letters without inventing a biography
The UCSF LGBTQ Resource Center glossary expands MTF as male to female and FTM as female to male. Gender Construction Kit notes that TS is sometimes used for transsexual. These explanations help with reading; they are not a complete description of someone's identity or circumstances.
Do not use an abbreviation to infer anatomy, medical treatment, sexual interests or readiness to discuss personal history. A short profile label cannot answer those questions. Likewise, it does not establish whom someone wants to date or what kind of relationship they want.
Follow the person's current description
If someone introduces herself as a woman, use that description rather than replacing it with an abbreviation you encountered elsewhere. If someone uses an abbreviation for themselves, that does not require you to use it for every trans person.
You might ask, “Is there a word you would like me to use when describing you?” Keep the question relevant to the situation. You usually do not need a full terminology discussion to ask about an interest or arrange a date.
Keep public and private wording separate
Ask before including identity information in an introduction, group message or photograph caption. A term shared with you privately is not automatically available for an announcement. Being familiar with a label does not tell you who else knows it.
If you misunderstand, correct the specific wording without turning the mistake into a demand for reassurance. “Thanks for explaining; I will use that term” can be enough. Do not argue that a dictionary gives you permission to override the person's answer.
Return to the actual conversation
Once the necessary wording is clear, talk about the person and the plans you share. Terminology knowledge should help you avoid assumptions, not become a test of whether someone fits a category correctly.
Sources and further reading
UCSF LGBTQIA+ glossary and Gender Construction Kit: transsexual. The dating examples are editorial suggestions; the sources are used for the limited terminology explanations above.