How long does SAT have to audit and collect, and how long does a taxpayer have to claim refunds?

The Tax Code (Decreto 6-91, art. 47 as amended by Decreto 4-2012) gives the tax administration four years to verify, adjust, assess, liquidate interest and fines and demand payment. Within the same four years the taxpayer may claim back what was overpaid or unduly collected (counted from the day after the undue payment) and may request the refund of VAT tax credit, in cash or as a credit against other taxes (counted from the date the refund could first be requested). Art. 48 extends the period to eight years when the taxpayer never registered with the tax administration; art. 49 counts both periods from the due date of the tax, and art. 50 lists what interrupts them.