The situation which you have described is that suppose the offered traffic is 87 erlangs. now from the erlangB table, to handle that traffic(87 erl) at 2% GOS we need 99 channels.
now if the OFFERED traffic is 87 erl that DOES NOT means that system will not block in busiest hour.even if offerd traffic is LESS than 87erl say 60ERL still the system can block because may be at a particular point of time there may be no free channel.GOS is a probability of finding ‘n’ channels busy.
consider a situation, where offered traffic is 103 ERLANGS with GOS=10% that too require 99 channels as required for 87erl with gos2% from erlangb table.
but i dont think system can carry more than 99 erlangs.