Why has the tax increased 8X the amount the current owners were paying? Heard it just happened in August 2012.

You did read the offering plan right?

Let's look at the annual summaries for the first unit to close:

June 2012: Annual property tax $3,300
June 2011: Annual Property Tax $326
June 2010: Annual Property Tax $13,408

Those're from before 421a kicked in, during, and the first 20% of it phasing out.

Here's from her Notice of Property Value:

Market Value = $270,057 -$9,406 $260,651
Actual Assessed Value = $121,526 -$4,233 $117,293
Actual Exemption Value = $119,083 -$27,203 $91,880
Transitional Assessed Value = $110,071 +$2,963 $113,034
Transitional Exemption Value = $107,628 -$19,156 $88,472
Taxable Value = $2,443 +$22,119 $24,562

The columns are for 2011/2012 tax year, the change, and for 2012/2013 tax year. Note the 20% drop in exemption value.

The 421a party does end eventually, and it's starting there. Then again, RE taxes are so complicated, I may've missed something.

Look how taxes increased for a unit whose 421a (if it ever had one) phased out before 2009. These are the "Annual Property Tax" lines from quarterly statements:

Jun-12 $15,200
Feb-12 $12,096
Nov-11 $13,254
Aug-11 $13,175
Jun-11 $13,175
Feb-11 $10,338
Nov-10 $10,338
Aug-10 $10,251
Jun-10 $11,270
Feb-10 ..$8,781
Nov-09 ..$8,781
Aug-09 ..$8,656
Jun-09 ..$8,656

That owner didn't have to figure out what the abatement was worth and pay up front for it. Much simpler....

You pay the mini-tax and then every two years you step 20% to the full value, but should New York reassess property values they phase in that part in over five years. Of course every year the building challenges, and if they win they pay a lawyer 20% of the projected savings and everyone feels better.

OK, so the "8X" is the jump from mini-tax to the first 20%.

Or $326 to $3300, and the $3300 includes some phase-in of increased assessed value.

It makes my head hurt. At least in a co-op, you're reminded of RE taxes only once per year, and see only your share instead of all the details.