Number of regions in bed, across annotations

[sahilseth]

I have quick question re, why the number of regions would change with annotations?

wc -l
 180,398 GRCh37/bed/Exome-NGv3.bed
 181,166 hg19/bed/Exome-NGv3.bed
 184,706 hg38/bed/Exome-NGv3.bed

Is it because some regions are not marked as gene/exonic?

Also, I downloaded a bed from roche, and the number of regions there are much larger. Could you direct me what process is used to go from vendor beds to these cleaner versions?

wget https://sequencing.roche.com/content/dam/rochesequence/worldwide/resources/SeqCapEZ_Exome_v3.0_Design_Annotation_files.zip

# SeqCap_EZ_Exome_v3_hg19_primary_targets.bed: 
# This file contains the design primary target (unpadded) in hg19 coordinates and gene annotation in the 4th column.
wc -l
242,232 SeqCap_EZ_Exome_v3_hg19_primary_targets.bed