Your understanding is largely correct, with a small nuance. Under Rule 42 of CGST Rules, a developer must reverse input tax credit (ITC) attributable to exempt supplies; such as sale of units after receipt of completion certificate.
Once this reversal is properly done:
The remaining ITC is treated as eligible ITC.
It sits in the electronic credit ledger at the GSTIN level.
GST law does not track ITC project-wise after this stage.
Can the balance ITC be used for another project?
Yes. The ITC left after reversal becomes part of the common pool and can be utilized for any taxable outward supply under the same GSTIN, including another real estate project.
Key points to ensure:
Accurate reversal: The calculation under Rule 42 (and Rule 43 of CGST Rules, if applicable) must be correct.
Eligibility: The remaining ITC should not fall under blocked credits as per Section 17(5) of CGST Act.
Compliance trail: Maintain proper working papers, as authorities may review project-wise allocations during audits.
Conclusion
After reversal, ITC effectively loses project-specific identity and becomes fungible at the GSTIN level. Therefore, the balance ITC can be legitimately utilized for another project, subject to proper compliance.