Hello TS,
I know you must be frustrated that Maestro had misplaced a 30year old guitar. I felt for you. However, we must know, no matter how much you rant, the guitar is not coming back. Why not you try to help yourself by posting a picture of your guitar, so we can look out for you.
I agree it's a mistake made by Zenguitarwrk.
However, please do not take an opportunity to flame them.
Evident: I'm pretty sure, they say it will probably be ready to collect on the day you wanted. I sent my guitars for repair job in Zen as well, I know very well the retail staff did not give you a certain date because they are not the ones doing the repair. Furthermore, it had nothing to do with the service of Maestro, because I believe they have many repair jobs before yours to complete before they can work on your guitar. So if you wants any express service, maybe you should pay an express service fee.