Until the US government terminates your status, you remain a permanent resident. Your I-551 is valid for work authorization.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
They are two separate questions. The old card is one issue. Having the old card did not cause your residency to be terminated. Having been outside the US for a period of years could lead to an allegation that you abandoned, and therefore lost, your residency. The fact of having been back in the US ten years may establish that you re acquired residency. I recommend meeting with an experienced immigration attorney to discuss confidentially and in detail the facts of your specific case.
This reply is intended only as general information and does not constitute legal advice in any particular case. This reply does not create an attorney/client relationship.
For all legal purposes you are a legal permanent resident until your status is terminated by the government; however if you would like to apply for citizenship or travel, the long period outside may cause an allegation that you have abandoned your residency. I agree with the other attorney's analysis, however, that since you've now been in the US for 10 years you probably re-acquired residency. Why not peak to an immigration attorney directly for the most helpful advice on the specifics of your case?
Gunda J. Brost Brost Law Office This advice does not form an attorney-client relationship and is merely informative. It should not by itself be relied upon to address a legal concern.