It isn't like passports - as long as you keep current, there should be no probem with having multiple licences - I know one person who has 8, all current. Check out how long type ratings last for - for example in JAA land, they last for 5 years after the date of last expiry (as do IRs). Some countries, such as Canada, accept other countrys' IRs as "currency" as long as you are flying in a commercial environment - you just have to make an annual report. Maybe Oz does the same.
Phil