Article 191 provides 'grandfather' protection for existing tax exemptions. Establishments and companies already granted exemptions under the old tax laws continue to enjoy them until their specified expiry dates. This includes the ten-year exemptions previously granted under specific articles of the prior laws. Crucially, it preserves the right to carry forward net losses realized during the first five years of an old exemption period indefinitely until fully set off. This ensures that businesses can rely on the incentives promised under previous regimes even after the introduction of the new unified Income Tax Law.