The reason why USCIS approved your extension for more than the period requested by your employer should not matter. Be grateful you got it. That's all.
You will be able to renew your H-1b for another 3 years if, due to visa retrogression you will be unable to adjust your status 6 months prior to the expiration of your now extended H-1B.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
You really would need to ask your employer's immigration attorney.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.
Sometimes the USCIS gives incorrect time frames on the approval notices. You are correct in being concerned about your immigration status now, rather than waiting until later to ask these questions. You should ask to meet with your employer's immigration attorney, or seek a consultation with an independent employment-based immigration attorney, to review your immigration history and address any questions you have. It will put your mind at ease, and you will have the correct legal answers to your particular immigration status. Best of luck.