This is one of the typical interview questions in JCL GDG. Many times confusion is there about generation Vs Version.
When we give (+1) in JCL. Only a new GDG will be created, but the version is V00(do not change). My discussion is when the version will be changed. The below example shows it.
//STEP1 EXEC PGM=IEFBR14
//DD1 DD DSN=GDGROOT(+1),DISP=(NEW,CATLG)
//STEP2 EXEC PGM=IEFBR14
//DD2 DD DSN=GDGROOT.G0005V01,DISP=(NEW,CATLG)
//STEP3 EXEC PGM=IEFBR14
//DD3 DD DSN=GDGROOT(+1),DISP=OLD
//STEP4 EXEC PGM=IEFBR14
//DD4 DD DSN=GDGROOT(+2),DISP=OLD
The result of the first run will be:
STEP1 ==> allocates GDGROOT.G0005V00
STEP2 ==> allocates GDGROOT.G0005V01
STEP3 ==> refers GDGROOT.G0005V01
STEP4 ==> refers GDGROOT.G0006V00
Refer to more details in this IBM link.