Google keeps indexing old site after migration, new site indexed pages dramatically dropped

Hmm, 2 months stuck on old URLs usually means Google hasn’t fully processed the redirects yet or doesn’t see enough signals to crawl faster. I suggest doing all this if you haven't yet:
Make sure your sitemaps only list the final URLs (a.com), not the old ones.
Check your internal links-- make sure they point to the a.com URLs, not b.com.
Build or earn a few fresh links to the a.com versions to speed things up.
If you haven’t already, submit the old URLs for removal in GSC -- sometimes helps Google drop them faster.

londate said:

Hmm, 2 months stuck on old URLs usually means Google hasn’t fully processed the redirects yet or doesn’t see enough signals to crawl faster. I suggest doing all this if you haven't yet:
Make sure your sitemaps only list the final URLs (a.com), not the old ones.
Check your internal links-- make sure they point to the a.com URLs, not b.com.
Build or earn a few fresh links to the a.com versions to speed things up.
If you haven’t already, submit the old URLs for removal in GSC -- sometimes helps Google drop them faster.

Click to expand...

Thanks for reply, i've done most, except the last one, I will try....

That kind of drop often points to Google struggling with consolidation.
Even with 301s and canonicals, if signals are mixed or crawl budget is skewed, the old domains can keep getting indexed.
Log file analysis might reveal if bots are still actively crawling b.com and a.cc more than expected.

It sounds like Google is still indexing b.com and a.cc because the 301 redirects or canonical tags might not be fully set up correctly across all pages. Make sure every old URL redirects properly to the exact page on a.com, and that canonicals on the old sites point to a.com too. Also, check your sitemaps and Search Console settings to confirm everything reflects the new site.
Backlinks from the old domains should pass value after redirects, but if those sites are still indexed, Google might treat them separately for now. This process can take time-sometimes months-for Google to fully recognize the migration.
I’d recommend running a full redirect audit (tools like Screaming Frog help) and monitoring Google Search Console closely.

uniquelydull said:

Make sure every old URL redirects properly to the exact page on a.com,

Click to expand...

we are not using 1:1 mapping for 301, but set a universal wildcard 301 redirect, in another word, any URL input with b.com prefix, will be 301 redirect to a.com, may this be a problem?

SEOPulse said:

After merging sites to a.com with 301s, index drop on a.com and rise on others may signal redirect or canonical issues worth auditing redirect chains, canonical tags, and crawl behavior closely.

Click to expand...

would you please tell some ways to verify if there is redirect or canonical issues?
we are using wildcard 301, in another word, any access with b.com will be 301 redirected to a.com.
canonical: we finished the verify of checking all the URL value in canonical field.

Please advise if any further investigation is required,
thanks!

uniquelydull said:

might not be fully set up correctly across all pages

Click to expand...

would you please advise any further steps or investigations we can do to verify whether 301 and canonical has been fully set sup correctly? Thanks!