In our previous articles, we reported two series of complex Zintl phase thermoelectric materials adopting the Ho11Ge10-type structures: Ca_11-xYb_xSb_10-yGe_z (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) and Eu_11-xKxBi_10-ySny (x = 0, 0.26; y = 0.86, 1.93) systems. In these investigations, we have tried to apply the p-type single or double doping for the anionic or cationic elements. However, since there was no attempt to apply the n-type doping for this Ho11Ge10-type phase, we planned to introduce n-type dopant using rare-earth metals for the binary Ca11Sb10. Four novel ternary Zintl phase compounds forming the ternary Ca_11-xRE_xSb_10-y (RE = La, Ce, Nd, Sm; 0.18(4) ≤ x ≤ 0.42(2), 0.14(1) ≤ y ≤ 0.41(1)) system were successfully synthesized by arc-melting, and their crystal structures were characterized by both PXRD and SXRD analyses. Given that we used the n-type dopants, we originally expected to provide more than 72 valence electrons (ve^-) for the title system. However, due to the non-neglectable Sb deficiencies found at the Sb3 site (Wyckoff 8h), the total number of valence electrons ranges only between 70.37 in Ca_10.58(2)La_0.42Sb_9.59(1) and 71.48 in Ca_10.82(4)Sm_0.18Sb_9.86(1), both of which were less than 72 ve^-. To understand this observed Sb deficiencies, a series of theoretical calculations using tight-binding linear muffin-tin orbital (TB-LMTO) method were performed. Eventually we reveal that the nature finds its own way to stabilize the given crystal structure by allowing a certain amount of vacancies at the Sb3 site (Wyckoff 8h) in the title compounds.