Plastic sheeting water barrier behind exterior trim

I live in a 16 unit townhouse complex in the Bay Area in California. The building exterior is a mix of painted stucco, painted wood trim and stucco stone, with some shingles and a flat roof, done in a 1970's psuedo Tudor style.
The association is starting a project to replace worn out trim and then paint the trim and stucco. As the trim is coming off we notice that behind the trim there is clear plastic sheeting protecting the plywood backing where the chicken wire is attached. The plastic sheeting is being removed but the contractor is not replacing the sheeting when new pieces of wood are being put back on. The wood called out in the proposal to do the job is "S3S Advantage Pine Plus" and is being screwed on with it primed on all sides.
The proposal also states:
"Remove loose caulking at all of the trim that can be safely accessed - Re-secure and reseal all of the trim with Sikaflex sealent".
I assume that they intend to keep water from getting to the plywood backing with the Sikaflex sealant but I'm not sure if this will work. My understanding of things is that sealant is a caulking that will keep water and the elements from getting behind the wood trim but I'm not sure if that can replace the plastic sheeting used for the water barrier.
Does anyone know what the code is for this type of job? Is the plastic sheeting necessary by code? Is it good practice to use regardless of what type of sealent is being used? Or is it no longer considered the right thing to do? Also would this type of thing be covered by local construction codes?
The contractor comes to us highly recommended but I'm concerned he is not doing the job as well as possible and that we will see water damage behind the trim eventually without the plastic.
\\Samson
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Building codes vary from place to place so you must ask at the municipal office that issues building permits. But codes are public information. There is nothing confidential about them, let alone secret.
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Carlsbad Springs
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