[David]

The symbolism of the singo (lion) on keris is indeed traditional and old, though i do not know when they first appeared on certain keris. Perhaps someone else has a better idea.
That said, keris are often re-worked in contemporary times, sometimes with the purpose of selling them to collectors in foreign markets. At least two of the examples you show, and perhaps the third as well, do not look to mae as if the lion was original to the blade. But many old and original examples do exist.