The ticket is valid until March.
Is March the last month when the ticket is still valid or the first month when the ticket becomes invalid?

Question

Answer

I agree with Shawn.

"The ticket is valid THOUGH March" would mean the ticket is still valid on March 31st.

In real life, I would hope that the ticket actually showed a precise expiration date, because language like this is never 100% clear and misunderstandings are possible.

Answer

It means on March 1st, the ticket is no longer valid.

Answer

you need to double check because it's unclear and seems to be important.