Hi Guy
Your man pulled the rug over on you so to speak. Seam sealing must be done immediately in most cases. Should the manufacturer state that the seams be sealed in say 24 hours the joint must be covered in this procdure. Take a core fr a carpet roll split then tape over the joint, this procdure must be done also in the case of an immediate seam so as to let the sealer dry with no dust or dirt. It is posible for you to salvage the problem at present by cleaning the joint with mineral spirits then applying the sealer ,yet i doubt that this would work. I feel that the best procdure would to patch the joint by inserting a piece directly over the joint yet one must be a master floor layer to accomplish such a task. too bad guy you got burnt however the problem is that your guys are not educated enough in those procdures, so I guess sad to say you have to shoulder some of the blame.
Have a nice day
Joe [master floor layer]
P.S. If I can help in the future just e-mail, Maybe I can put off some sort of course for your installers