Why do course class beginning and ending dates not match the course length descriptions on ATRRS?

ATTRS is GIGO
Garbage in Garbage out.
It is populated by someone at that school house with special ATRRS access to edit the course description and supporting info.

I ran the Schools section for 1st Cav as part of my G3 SGM duties.. and we ran into ATTRS course info being worng, outdated a lot. The Fix was many times done by a school house person that had no actual knowledge of the course.. but was just the person responsible for updating ATTRS
Bottom line, you will often get info in a welcome packet that is more updated, more correct than a ATTRS course description. ..

I've been to a school where they don't match. Go with the achool house dyaes. Everyone in my class had their 1610s created off the attrs dates and we were given 72 hours to have them amended to match the school house or we were sent home.

Give employer all the info you can. Explain the course dates as listed, as well as the other calendar info you have. Play it straight w your employer, they will understand there is some travel/arrival time in there. When you FINISH the school, you will of course end up with travel voucher documents, pay docs, and orders with actual dates. Allow yourself a day or so of return cushion for planning ... As a civilian (as well As military) supervisor, I would prefer a rested employee returns on time on Monday as planned, rather than last minute no show because class ran 1 day late, problems w making flight connections, Etc.