Under 8 CFR 204.5(e)(1) the priority date of an approved I-140 is retained for a later EB-1, EB-2 or EB-3 petition unless USCIS revoked the approval for fraud, willful misrepresentation, material error, or an invalidated labor certification. Since the rule that took effect January 17, 2017, an employer's withdrawal or closure doesn't cost the beneficiary the date.

8 CFR 205.1(a)(3)(iii)(C) and (D): a withdrawal or the employer's closure 180 days or more after the I-140 was approved, or after an I-485 based on it was filed, no longer revokes the approval automatically. Inside 180 days it does, which matters for extensions and for using the I-140 as the basis of a pending I-485. It doesn't affect the priority date.

INA 204(j) and 8 CFR 245.25: once the I-485 has been pending 180 days, it may be approved on a new offer in the same or a similar occupation, filed on Form I-485 Supplement J. Whether the new job is same or similar is USCIS's determination.

Before the I-140 is approved, a move usually means a new PERM with the new employer. Once it's approved, the priority date stays yours for a later employment-based petition unless USCIS revokes the approval for fraud, a willful misrepresentation, an invalidated labor certification or a material error (8 CFR 204.5(e)). An I-485 pending 180 days or more can move to a same or similar job (INA 204(j); 8 CFR 245.25). In H-1B status you can start with the new employer once it files a nonfrivolous H-1B petition for you, or on its requested start date, whichever is later (8 CFR 214.2(h)(2)(i)(H)). Enter your dates above to see where each one stands.

No. The dates are arithmetic on what you enter and the regulation each rule comes from. A revocation's reason, a job's similarity and the effect of prior filings are for the attorney handling the case.