Laundress is "SPOT" on again!
I worked in dry cleaning (years back) and we had accounts with some of the local hotels, including their in house restaurants.
Aprons, Polo shirts (part of the uniforms) as well as black slacks and white shirts, black ties ect all came in with food and grease, you name it we saw it!
Since certain stains are water soluble, AKA..the food, blood, perspiration, and general dirt, they were fist washed and dried. The reason was because it was too hard to see what was what to even try to pre-treat.
Once washed and dried, the oil stains could be clearly seen. Usually that point, all stains were gone, except the oil! They then were run through the dry cleaning machine (solvent) which would pull out all remaining oil. Then sent down the line to the pressers and finishers. (Except the shirts, handled a little different)
Laundress:
Dear, I was waiting for someone to mention vintage Fel Naptha LOL