The general rule in coaching is that a coach cannot re-sign for a new team after being fired unless the collective bargaining agreement provides for it.
Serie B added a note to the collective agreement, thus allowing for this possibility. This option has blocked several coaches who now have the option to move to another club. There are no restrictions on categories: this is why a coach fired from B will be able to move to another club from B, as well as from A or C.
Source: Tutto Mercato Web

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