The department heads regularly do a walkabout around the progressing set construction. They are looking for flaws and potential problems. If you haven't been a set designer yet, and you want to, you will soon find out that your drawings will often be modified, for various reasons, as the sets get built. Sometimes it happens verbally during the walkabout, as they realise technical issues. Sometimes the set builders cut corners for time and budget.
As a set designer, I often found myself missing out on the group cruise. Often the revisions happened without my knowledge. I soon found it was imperative I cruised, too. Only if I cruised the set would I spot all the discrepancies and revisions. I knew every detail intimately. Things the critical eyes of the heads on a walkabout would miss. Things they weren't looking for. Technical set detail things. Small things. Some things didn't matter. Some things did.
So they chose a different moulding because the one I picked was out of stock. No one would likely notice or say anything. Things like that don't matter.
But the time they made the 'as-stone.' steps with a straight riser and a 1" nosing because it was cheaper and quicker than bullnosing canted risers, did matter.
Often, the designer or art director will miss those small modifications. Things like that may seem petty, but it is embarassing for a designer to later have someone come up to them and point out that their stone steps looked like wood steps painted like stone.