@Jean-Michel ********
You are confusing two separate things.
One is the validity of the VISA you got from the thai consulate <- that's what let's you IN to the country and is good for a year from the date it was issued
The other thing is your entry stamp <-that's what let's you STAY in thailand, and on the O-A visa you have you get stamped in for ONE year every time you enter the country (for the validity of the visa),
IF you exit//re-enter just before the VISA expires (in your case July 2019) you would get stamped in for a whole new year (even though the visa will expire in July).
The entry stamp lets you stay in the country and the VISA lets you in and controls how many days you get stamped in for