Need Help Dating This Cob

...I just bought this on MA Shops, German dealer who had it incorrectly identified as being struck in Toledo, Spain. I attempted to correct their description, & my (correct) identification was politely declined.
...so, I bought it (@ a really good price).
...It's a Potosi (Bolivia) 2 reales, struck by assayer J. J. de Tapia (hence the " T " assayer's mark, mistaken by the seller as a Toledo, Spain mint mark) ...
...The rather large " Z " (substituted for an Arabic " 2 " / 2 reales) is found on Atocha (shipwreck / 1622) 2 reales, assayer " T ", & potentially identifies the minting date between 1618 (Tapia's 1st year as assayer) & 1622 (Atocha sinks) ...
...the complete date is missing, but some numerals (1s, & the bottom of either an 8 or a zero) appear in the normal position (between 9:00 & 12:00, on the reverse / cross side) ...
...the " T " (9:00,obverse / left of shield) seems to have an unusual base, almost as if it was struck over an " L " (unlikely, as assayer " L" was there some 40 years prior) ...
...My3 questions are these:
1. Was this cob struck between 1618 & 1622?
2. Is the "T" over-struck onto another letter?
3. Is the date either 1618 or 1620?
Any thoughts & opinions will be greatly appreciated ... thanks for looking ...John