It seems that many now agree that in early versions of the Chinese script 人千身仁 and 年 are all in the same xiesheng series. But, my question is if, what are the _semantic components_ of these various characters. I don't necessarily mean this question in terms of 'what are their kaishu' transcriptions, but rather 'what other examples of say the "belly" semantic that distinguishes 千 and 身 in the Chu script?' etc.
Answer must probably address sinograph per sinograph, as we deal here with a long period (late 4th c. BCE to Later Han dynasty?). Boltz 1994 illustrated the tendency to syllabic writing, or, in other words, that a semantic determinative may also be missing entirely or being unrelated to the intended word meaning. Scribal variation may be expected.
Baxter & Sagart 2014 OC, 238f discuss the case in question. The phonetic det. (writing a syllable of the form **NING that can be modified by affixes etc) is either 人 or 千 (wherein is enclosed a 人; sem. det. is here a horizontal stroke); in nián 秊(年) phonet. det. is 千, and sem. det. is hé 禾); Chu style 仁 is written either with phon. det. 身 or 千, adding the sem. det. xin 心, displaying variation.
For other sinographs with the element 身, see He Linyi Zhangguo guwenzi dian, pp. 1137ff.
But it sounds like you do not see 身 as having a phonetic determiner 人 plus a semantic, which by implication is how Baxter & Sagart understand it.
in He Linyi, p. 1137f. you can see that 身 could be seen as having 人 or 千 as phonet. det. and that in some cases it is read in the meaning 信.
However, not clear to me if I understood the original question well, maybe you could reformulate, or specify what you wanted to know?
Perhaps the "Zhuan Zhu" 转注, from traditional "Liu Shu" 六书, could be used to understand the structure of these characters. There are not necessary to treat the characters as a combination of phonetic and semantic parts. It's kinda like Zhi Shi指事, making difference by adding a stroke, but in Zhuan Zhu, or in the cases you mentioned, the new created scripts are as well phonetically related to the original ones.