It can be frustrating and why I'll soon call ahead with my 13 Mini to ensure the Apple Store has one in stock first, something I suggested to a poster a while ago who had to travel couple of hours for exactly this. I know this isn't exactly the situation you had OP.
A few years ago I sat in one of the two Apple stores in my city waiting for a battery replacement. Was all booked in, handed the OG SE in and waited an hour or so. Meanwhile I got chatting to another waiting customer with the same model, also getting a battery replacement.
So after this hour an Apple employee came up to me and told me they don't have a battery in stock, obviously the only one in stock was given to the customer I chatted to before. I commented on my frustration waiting an hour to be told this but these things can happen when concurrent event like this occur. This was frustrating but not what annoyed me.
At that stage I asked for a supervisor and asked how we can now resolve things going forward? I was prepared on my only day off to travel to the other side of town to the other Apple Store, if only they could please check for me if they have the battery in stock so I don't waste my time and travel expenses again. Well, the answer was that their system didn't allow to look into the stock of another Apple Store! I then asked if they could call the other store to ask and the young and somewhat arrogant supervisor replied that they're unable to call. Admittently I did start fuming at the absolute lack of customer service and their unwillingness to try help. I just replied that phones and communication devices are after all their business so this surely must be possible?!
I did end up travelling immediately afterwards to the store much further away. They had to order the battery and we made an appointment after a few days to have it installed, they also looked after me regarding the overall price. Suffice to say I have blacklisted that original place, as overall staff attitude over the years really has reflected the experience I had of that one day and this wasn't an isolated incident.
Since then I've had some AC+ claims with my MBP and the demeanour, customer service and quality has always been excellent at the store across town. It just became obvious that the workplace culture at the initial place was rather negative amongst most of the staff and their attitude dealing with customers reflected this.