It looks very much to me that you’re trying to approach your table the spreadsheets way, not the Coda way. In spreadsheets it doesn’t matter how you spatially organize your data in rows and columns as long as you’re able to make sense of it yourself. In Coda, each record is strictly a separate row, and columns are just properties of that record.
While in some cases it makes sense to treat Jan/Feb/Mar/etc checkboxes simply as separate and predefined properties of one record, here it looks like each cell (a status per row per month) should be a record of its own. So you create a table with this structure in mind, and one conditional format:
and then make a grouped view out of it to get the layout you want
Now, there’s one valid reason when you cannot use this approach: when you want to be able to copy this view and paste it into Sheets/Excel. When you do that, instead of a grouped view the original one will be pasted (groups are not preserved when copying to sheets). In that case you’ll have no choice but to make a table with months as separate columns and set up conditional formats individually on each column.