Nandi, Uasin Gishu and Elgeyo Marakwet, previously opposed to BBI, are likely to join the crowd of supporters and vote for constitutional change.
Extensive public participation is scheduled before votes.
Turkana and Kericho assemblies also had a change of heart and were expected to approve the Bill on Wednesday.
The MCAs are allies of Deputy President William Ruto and have found themselves in a tricky situation after the total number of assemblies approving the Bill stood at 38 on Tuesday evening. Approval by 24 assemblies is needed for a referendum after a debate in Parliament.
“We have scheduled public participation next week," Uasin Gishu Majority leader Josphat Lowoi said.
Ruto has called BBI not a priority in a country ravaged by Covid-19. Most MCAs in the Rift Valley - Ruto's backyard - had pledged to shoot the Bill down.
Some of them, now isolated, are rethinking their plan so they won't be left out.
Behind-the-scenes lobbying was underway by DP allies to have MCAs back the Bill and not leave themselves exposed, sources told the Star. They were released from their pledges.
The Nandi county assembly had been expected to reject the Bill but is likely to approve it on Thursday on the advice of senior politicians.
“We have done public participation and the MCAs will have the opportunity to debate the Bill and vote," Speaker Joshua Too said.
Uasin Gishu Speaker David Kiplagat said public participation is scheduled on Friday and the vote is expected to be on Tuesday.
In Elgeyo Marakwet, public participation will be on Friday and the vote next week.
Jubilee secretary-general Raphael Tuju had summoned 17 nominated MCAs from Uasin Gishu to party headquarters on Friday last week and told them the Bill must be passed. Voting is expected next week.
The nominated MCAs attended the meeting with Tuju in Nairobi and will lead the campaign for the Bill in the assembly.
Uasin Gishu is Ruto’s home county and the assembly's 48 MCAs are mostly allied to the DP.
Only Baringo MCAs rejected the Bill last week in an acrimonious session where ward reps allied to Baringo Senator Gideon Moi wanted the assembly to approve the Bill.
It's likely only Baringo will go on record as having rejected it.
Close allies of the DP were meeting to discuss the future after almost all assemblies backed the BBI Bill, against expectations.
(Edited by V. Graham)
