Can my friend still use his DTV visa for training in Thailand despite a long absence?

A friend with a DTV visa is unsure if he can still use it after not being able to come to Thailand for about a year. The consensus is that the visa is valid for five years from the issuance date, so he can use it when he eventually travels. However, he will need to re-enroll in a Muay Thai training program upon arrival, as this may be questioned by immigration officials. It's also noted that there may be some scrutiny or checks since this situation is not very common.