Can I recycle ffmpeg2pass-0.log - ffmpeg

Question

Can I re-use 2 pass logs?
That is to say: I am doing this, but I wonder if I should be doing this. ie: does a -pass 1 that had different crf/b:v parameters from -pass 2 output produce the same results as always uniquely encoding both passes for every input?
I have a feeling I shouldn't be reusing pass1.
Say I am doing tests, and for the same input file produce multiple 2 pass ouputs with varying constrained bitrate/crf variants...
eg:
constrainedQ-br9M-crf12.webm
constrainedQ-br12M-crf18.webm
constrainedQ-br14M-crf18.webm
constrainedQ-br16M-crf18.webm
Is it ok to detect the prior log file, check that it was produced for the same input file, and re-use it by skipping -pass 1 for subsequent renders? (in which case ffmpeg finds the existing log and appears to use it for pass 2)
Or
Should I be re-generating the pass 1 log whenever the bitrate or crf changes?
[edit] everyone loves a bit of context code
f_rm2passFilesVP9() {
rm \
"${input%/*}/ffmpeg2pass-0.log" \
"${input%/*}/ffmpeg2pass-0.log.temp" \
"${input%/*}/ffmpeg2pass-0.log.mbtree.temp" &> /dev/null
}
...
f_2passLogForThisInputExists() {
if [[ "$input" == $(cat "${input%/*}/.priorInput" 2> /dev/null) ]];then
echo 1
else
echo 0
fi
}
...
if [[ 0 == $(f_2passLogForThisInputExists) ]];then
echo " ENCODING CONSTRAINED QUALITY br:$br crf:$CRF - PASS 1/2"
trap "f_rm2passFilesVP9" 1 2 3 6
ffmpeg -hide_banner -y -i "${input}" \
-c:v libvpx-vp9 -pass 1 -b:v "$br" -crf "$CRF" -threads 4 \
-tile-columns 6 -frame-parallel 1 \
-an -f webm /dev/null
echo "$input" >"${input%/*}/.priorInput"
trap "" 1 2 3 6
else
echo "REUSING - PASS 1 FOR THIS INPUT - PASS 1/2"
fi
echo "ENCODING CONSTRAINED QUALITY br:$br crf:$CRF - PASS 2/2"
ffmpeg -hide_banner -y -i "${input}" \
-c:v libvpx-vp9 -pass 2 -b:v "$br" -crf "$CRF" -threads 4 -speed 2 \
-tile-columns 6 -frame-parallel 1 -auto-alt-ref 1 -lag-in-frames 25 \
-c:a libopus -b:a 64k -f webm \
"${exportName}"

Answer 1

This should be OK if you are simply giving it more or less bitrate. I do this sometimes, but I also use a lot of zones, so I usually just rerun first pass because I know zones will definitely make a difference in the first pass file. If I add a zone after the first pass file is created the it will apply the difference in bitrate across the file and if I do it before then the zone bitrate modifier gets applied only to the frames specified. Since I think you are simply giving the file more or less bitrate then the distribution should be pretty much the same. I would say only rerun first pass if your second pass is going to much higher bitrate, like 20% or more. Better just to run first pass at the highest bitrate you intend to encode, if possible.