Such insurers may invest in obligations of the Dominion of Canada, or the Commonwealth of Puerto Rico, or of any province of the Dominion of Canada, or of any political subdivision of the Commonwealth of Puerto Rico, or obligations for which are pledged the faith and credit either of the dominion, or the commonwealth, or of any province of the dominion, or of any political subdivision of the commonwealth, for the payment of principal and interest, if within 10 years immediately preceding the investment such province or such political subdivision was not in default for more than 90 days in the payment of principal or interest upon any legally authorized obligation issued by it.