Trying to calculate grav in an overlycomplicated cider making process.


Okay, folks. It's my first time making cider (long time making beer). and I messed up but fixed it. However, I cannot calculate the gravity now because I was adding stuff, modifying and so on. Please help me figure out if my calculations are correct:
First, I made 3 gallons of cider by adding Camden tabs the day before, then heating to 190F for a bit (sterilization overkill?), then cooling and pitching a pack of Safale US05
The gravity was 1.045 which my ciderloving friend said was too lowshe wanted some strong cider.
So I added 1 lb of sugar (dissolved in some boiled water). I know, in retrospect: what a stupid thing (which I was told by a "soft" cider vendor).
When it had fermented down to a gravity of 0.098, I added another gallon of cider (1.045 grav). It fermented to about 1.003
Determining it to be still too solventy, I added about 2/3 Gallon of tart apple juice (unpasteurized) (grav: 1.048).
now, nearly a year later, the grav is an even 1.000
This is my calculation, based on gravity points of the ingredients to figure out what the OG would have been had I put all of this in at the beginning
Grav of the initial mixture: 1.045 of 3 Gallons
1lb sugar into 3 gallons = 1.045/3 gal = 15 points more.
another gallon at 1.045. Now this divided by 4 gallons = 11.25 pts.
the remaining 2/3 gallons of apple juice, at a grav of 1.048, goes into what is now 4.7 Gallons of cider. That's 1.048/4.7 let's just say an additional 10 points.
So, in total : 1.045+15+11+10 = 1.081 as what the starting grav would have been had I put this all together.
With a FG of 1.000, this means 81 X .131 = 10.6 ABV
Is this in any way an accurate estimate?
