Guy, the statement "The odds most likely are very good that it may never happen again" may be a a bit misleading for a number of reasons. Having had Lyme disease does not provide protection against re-infection, many people who have had Lyme and been treated get renewed infection after additional exposure. Also Lyme is not the only tick-borne disease that can cause severe illness; bartonella, babesia, etc. are others that may or may not be transmitted during alternate tick bytes. Finally, there are different strains of Lyme that manifest itself in different symtoms and treatments.
It's a nasty business. To be conservative I would treat each exposure as a new one and act accordingly.