Issue on NumberSequence(Generating the Alternative numberseq)

Hi All
I have one doubt in generating the numbersequence.

Actually the problem in my report is … For the particular transcation If i am doing renew on different account. so it have to generate the new fixed deposit number .
Here we are taking FD_1465
7658.1.docx (161 KB)

So when we click on renewal on different account . it will open small form containing(generating) the Fd_001469.

4743.2.docx (152 KB)
But Here Fd_001466 have to generate.
But here its skiping the Fd_001466, Fd_001467, Fd_001468 and generating Fd_001469.
Can u please tell me why it is happening like this.