I've not bothered to get licensed outside of California because just within California is plenty enough regional variation for me to keep track of...

If selling the property, I would make sure the listing had the Appraisers square footage listed, note the variation in the Agent Remarks, and provide proof of additonal SF to any potential buyer. 

May need a zoning variation or special use.The zoning district may impact you for example the district might be approved for commercial use even though it currently is residential.  

question (or a 1,000 variations thereof).  

I had tried about every variation but the correct one. 

Every time I've had bids on plumbing I've been surprised at the variation.

I have used several variations of rehab calculators, including one we modified and have been using for several years, but I really like the new BP calculator.

Since there is so much variation i'm fairly confused on which way to proceed.

I have a similar 1926 Spanish bungalow in LA (3bed 2 bath, 1300sqft, single level), that i just rebuilt completely, so here's my 2 cents1. with plumbing and sewer, make sure that you insect and assess the main drain line form house to street sewer - in houses of that age, they are cast iron and are often buried under a concrete driveway. if it needs to be replaced, make sure re-pavement of driveway is accounted for2. houses of that age have often started as 2bed 1bath and then somewhere along the way been converted to say 3/2 - mine was in the 70's. ask whoever inspecting the foundation to pay attention to the way it's laid out - variation in crawl-space hight, floor joists and different materials used for pillars that house sits on could point to an addition. flat roof over one of the bedrooms or bathrooms in an otherwise house with an attic is another sign it's been added. either way, check with the city that those additions are legal/permitted3. termite damage and dry rot in California and Arizona is a given - in any house, especially that old. as you walk around the rooms, stop in each corner of every room and jump up a few times - if the floor is soft and even a sign of weakness, i bet you you'll have to re-drywall, remove subfloor and repair floor joists in at lest half of that room. just a simple "poking wood for termites" test from the crawl space often misses that. i like my jumping test as well5. size and age of electrical panel - yes, but also age of main electrical wire runs is important. those are usually suspended in crawl spaces or laying on top of ceiling joists in the attic. old wire should be replaced as it's a potential fire-hazard surrounded by all the old fluffy insulation that's in old attics - speaking of fluffy insulation, i hear in some cases it could contain asbestos, so wouldn't hurt to checkfyi, just installed central air in my house and my best estimate - had 7 total - came through Costco at just under $7000 for a 3-ton Lennox system (heat and cool), all new ductwork, permit and inspections. curious as to what your HVAC bid was

There's enough variation that I keep mine 7 years.