At this point, it won't matter much because he really won't have enough time to build a full immune response generated by the vaccines. In order to be most effective, they have to be given at proper intervals and boostered. It is not ideal to give all shots at once for a few reasons. Certain illnesses are better grouped together for maximum response (like strains of EHV or types of encephalomyelitis) others are fine in conjunction with multiple types (like a 5 or 7 way) you don't want to give a modified live vaccine at the same time as a killed type. Other vaccines can stimulate a stronger response when given after a horse has developed immunity to a similar type of illness. For instance, there has been some discussion that West Nile vaccine has a stronger and more lasting response when given 10-14 days after EEE/WEE/VEE. So I have always done my WNV after a multi-way for that reason and because I use a modified live. Basically, the only reason vets will give multiple shots is really owner convenience.
I would say as long as you have a negative coggins (Heath if required, although it's a pretty worthless piece of paper) and your horse appears healthy and can stay separate from the other boarders horses, he should be fine.
Personally, I don't care if other people's horses have a vaccination record because the record really doesn't indicate whether the vaccines were given properly or if the horse has built up any immunity. All I can do is vaccinate mine. I vaccinate my entire herd as if they travel and I have them grouped according to risk as best I can. This way the show horses are less likely to get an on-farm horse sick. I also am a germ-nazi when travelling and practice as much bio-security as I possibly can.
For your short term situation, I would avoid exposure to a horse who travels a bunch; looks unhealthy in some way; and/or is exposed to high risk horses. This is why boarding situations without adequate separation/quarantine are not ideal places.
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Thank you so much! My friend has a large facility, and only a few horses from what I know. She just opened this summer. I'm sure she's got a quarantine area. (Yeah, he'd only be their for a week.)