Except ZrPdGa, only trivalent rare-earth and mixed valent Ce 3+/4+ were found to stabilize the LaNiAl type structure so far, and no phases with mix-valent Eu 2+/3+ or Yb 2+/3+ with this structure type have been reported. Importantly, Ce 3+/4+ valence fluctuation is observed in many phases like CeRuAl and CeRhAl. The valence fluctuation in rare-earth metal seems to play a critical role in the stability of the LaNiAl type structure, since mixed valent Ce 3+/4+ are additionally observed in some solid solutions like CeRu1-xNixAl and CeRu1-xPdxAl. The LaNiAl structure type is best viewed as an intergrowth structure build with slabs cut from the hexagonal ZrNiAl, and the orthorhombic TiNiSi types. In the series RECdPt, trivalent rare-earths were found to favour the hexagonal ZrNiAl type, while divalent Eu and Yb favoured the orthorhombic TiNiSi type. Therefore, the LaNiAl type structure may prevail when the stability factors of the two parent structures are competing.