This would suggest that this has been an ongoing problem , if the problem was only with a specific batch of parts I am sure that Bell would know exactly which aircraft were shipped with these batches and which ones were shipped as spares. It is inconceivable that an aerospace manufacturer would not have this information available through their ERP system. But on re reading the AD the TIS limit makes no sense , it would have made more sense to specify a range of serial numbers or spares delivered in a certain date range.
edited for spelling