However you never know if the tile in the right place can be used until you get there.
I got caught out with something similar on the only ‘real’ installation I ever did.
The company I worked for at the time had a contract to install a server and set up backups etc. for a medical company. They had an office and a lab in the same single storey rectangular building, with the rear two thirds holding the lab, and the front third holding the office / reception. The router and office computer were in the front right corner of the office, and the server needed to go in the front right of the lab. Sounds easy enough, run the cable up the wall, through the false ceiling and over the partition wall, then down the other side.
For some reason, whoever had installed the partition wall had taken it right up to the real ceiling and sealed the top too. It had been installed after the company had been there for a while, and they didn’t know why it had been sealed. They’d left about a four inch gap over on the left hand side of the wall for cabling. I ended up climbing along a selection of chairs, tables, and ladders to get the cable into the ceiling, then had my boss on a table in the lab to pull some cable through the hole. We then had to swap sides as I was the smallest, so that I could climb around the unmoveable lab equipment and feed the cable back in the lab side.
We didn’t think to check if there was anything else in the way, and about half way across the room we hit a beam. No idea why it was there or what it was for, but we had to go around it. What should have taken an hour at most took us a few hours of climbing and swearing >.<
I can’t remember why we couldn’t drill through the partition wall, but the beam was one of those big steel things, and seemed to be randomly fixed to the ceiling for a metre or two.
The boss put a new rule in place afterwards to double check cable runs, and not to rely on the customer 😀
