There are several branches down from Z140,Z141 ...  Y6231+  A196+ [aka Y5497]  A1374+ ... plus two further main branches, F2642 [aka S2169]; and Z2535 [aka S1953]. If you are positive for any SNPs down one branch, you cannot be positive for any SNPs down the other branch. The further down a branch you go, the nearer to the present day you move.
Most of the SNPs come as a result of Y-genome sequencing, from Public Genomes, FGC Full Genomes, and FTDNA Big-Y.
If you require any advice regarding the testing of SNPs and STR markers, please do not hesitate to ask one of the I1-Z140 Project Admins.
You are invited to join the Facebook 'I1-Z140 Project' at: https://www.facebook.com/groups/I1.Z140.YDNA.Project/
'I1-Z140 Project' at YFull.com: http://www.yfull.com/groups/i1-z140/
YFull 'I1-Z140 Tree' http://www.yfull.com/tree/I1a2a1/
The most-likely-STR-trees show the most-likely phylogenetic trees; here for Z140 and it's subgroups: F2642, AS-6 Harvey et al, AS-5, AS-3, AS-EE, Small groups, AS-814, L338
Note: the most-likely-STR-trees show the most-likely phylogenetic trees. In some cases SNP's or multiple STR's (dependent on the mutation rates) give strong evidence for the lines. In other cases only one mutation of an STR with high mutation rate give indication for a separate line. The lines will improve in quality if more people measure 111 STR's. People in the small groups and individuals are also advised to measure SNP F2642 and Z2535.
A haplogroup is a group of descendant individuals from a single founder who all share a common SNP mutation. Individuals can test for these SNPs to determine their haplogroup assignment, which is often reflective of distant geographic ancestry. Membership in a particular haplogroup thus indicates broad population and geographic ancestry while other mutations in descendant haplotypes can reflect recent genealogical ancestry.
A SNP (single nucleotide polymorphism) is a variation in DNA sequence between individuals involving a difference at a single base-pair. SNPs generally have lower mutation rates than STRs and are often sufficiently stable to robustly define haplogroups.
"Private" SNPs on the Y chromosome correspond to relatively recent mutations that have not yet been observed in a significant number of other individuals in the same haplogroup. Some of these will eventually be incorporated into the Y-tree with further research. Others may provide clues about recent genealogical ancestry.
STR (short tandem repeats) are a type of molecular marker consisting of short DNA letter repeats (such as CACA). These markers have a high rate of mutation and are accordingly useful in determining population genetic differences. In the Y chromosome line, SNPs and STRs in conjunction serve to show differences between individuals and groups in their DNA lineages. In short, STRs are one part of the puzzle in everyone's Y chromosome DNA heritage.