Yes you are saying right but it happens on weekend only.
If you search for tommarrow there is availabilty in duronto and availablity in GR tatkal is 283 in JB there is current availability around 30. This shows that a person who planned his journey on last minute he can also get ticket in these trains on weekend there may be problem but on other days there is not a big issue. there are many other trains also. I have personally seen that for SBC, TPTY,& VSKP that you can get your seat cnfrm 1 day prior to the journey.