For the following equivalent questions, you choose
whether-or-not the 3 variables in a clause must be distinct.
Is there an integer $k$ such that for all 3-SAT formulas $\mathcal{F}$ without negations,
if every $(\leq k)$-clause sub-formula of $\mathcal{F}$ is 1-in-3 satisfiable then $\mathcal{F}$ is NAE-satisfiable?
Equivalently, is there an integer $k$ such that for all
3-SAT formulas $\mathcal{F}$ without negations, if $\mathcal{F}$ is not NAE-satisfiable then
$\mathcal{F}$ has a $(\leq k)$-clause sub-formula which is not 1-in-3 satisfiable?
(The Fano plane shows that $k$ can't be less than $7$.)
**Motivation:** That is the "low end" of my question
[on cs.stackexchange](httphttps://cs.stackexchange.com/q/51828/12859) which was inspired by the
possibility of generalizing [Schaefer's dichotomy theorem](https://en.wikipedia.org/wiki/Schaefer%27s_dichotomy_theorem)
to constraint satisfaction [promise](https://en.wikipedia.org/wiki/Promise_problem) problems.
Specifically, for _the simplest_ non-trivial promise-constraint,
with m being the size of the input set, I have neither managed to
find evidence for it being in [promise](https://complexityzoo.uwaterloo.ca/Complexity_Zoo:P#promisebqp)co[QIP\[2\]](https://complexityzoo.uwaterloo.ca/Complexity_Zoo:Q#qip2)T[IME](https://complexityzoo.uwaterloo.ca/Complexity_Zoo:N#ntime)$\hspace{-0.02 in}\big(\hspace{-0.04 in}$2[o](https://en.wikipedia.org/wiki/Big_O_notation#Little-o_notation)(m)$\hspace{-0.03 in}\big)\hspace{-0.04 in}\big/\hspace{-0.04 in}$[q](https://complexityzoo.uwaterloo.ca/Complexity_Zoo:Q#qmaqpoly)2[o](https://en.wikipedia.org/wiki/Big_O_notation#Little-o_notation)(m)
for infinitely many m, nor find evidence that it's not solvable
in [co](https://complexityzoo.uwaterloo.ca/Complexity_Zoo:C#conp)N[TIME](https://complexityzoo.uwaterloo.ca/Complexity_Zoo:N#ntime)(O(1)) on essentially the most basic [word RAM](https://duckduckgo.com/?q=%22word+RAM%22+complexity).
The former applies even when each variable occurs exactly twice
and "many m" gets replaced with "many _even_ m" (since 3 is odd),
and the latter applies even when [negative literals](https://en.wikipedia.org/wiki/Boolean_satisfiability_problem#Basic_definitions_and_terminology) are allowed.