I know that Russia and the United Kingdom imposed limitations (i.e. children and grandchildren through sons of sovereigns). But to the best of my knowledge, titles were indefinite in all the German and Austrian houses, to those persons of legitimate male-line descent. This, of course, meant in addition equal marriages.
Case in point: Prince Eugen of Bavaria was (in the male line) only a great-great-grandson of a king. Although his paternal great-grandfather (Prince Luitpold) was a DE FACTO sovereign, serving as regent of the kingdom, Eugen's nearest direct ancestor in the male line who was a sovereign on a DE JURE basis was King Ludwig I. Yet, I believe he was styled with the title of Prince, with the qualification of Royal Highness. Is this correct?
Perhaps, in the royal houses of Sweden and Denmark, males far down in the succession tended to marry morganatically ...