SIP providers usually sell numbers in contiguous series for businesses. For example, if your company buys a block of 50 numbers, the SIP provider then allocates XXX-5100 to XXX-5150.
But since you're keeping this strictly internal, you don't have to worry about that.
It's only minor if the data points in this breach are used by themselves.
Once you aggregate this with other data breaches, you could end up with a much bigger capability to target anyone in this breach.