Data cleaning, HELP!

Please download the attached excel workbook.

It has data in the following format

A               B                  C                  D
102.5       500                20                 501
105.7       499                21                 501 
105.9       498                20                 501
107.0       496                20                 501 
108.6       495                20                 501
110.1       493                21                 501 
....           
...
...
467.5       164                20                501

I want to arrange this section of data in the following format:
1. Each row is a record, so I would like to keep the rows as a whole
2. It should be arranged in decreasing order of column B (and increasing order of column A). I have already taken care of this operation.
3. I want it to fill the missing numbers in column B (497 and 494) in this example. That new row (with the new numbers in column B) will not contain any other data, i.e., columns A, C and D should be blank.

My problem is that there are many such sections of data in the worksheet arranged side by side with one column to separate them (as you can see in the WB). In each section's column B, different numbers will be missing.

For all sections, I want the second columns to have numbers ordered in decreasing fashion between a certain range, say 585 (at the top) to 475 (at the bottom) (see worksheet please). Therefore, the length of each table must be the same.

I have come to this stage after a lot of data manipulation and this is the last bit. The looping structure seems to confound me the most, can someone help me??