Poopsy Woopsy

You are on your way to the board and I would suggest hiring a agent/lawyer right now. I fired my VSO because it was going to be over a decade before I see any resolution. You can read my current status here
Known legal help here at Hadit are Katrina Eagle, David Anaise, AskNod, GloverLuck to name the few.

Hello,
It is inspiring to see your dedication to your husband's cause, and equally frustrating to see veterans in a seemingly endless circle of claim-denial-appeal-denial-appeal...  I applaud your determination.
BVA hearings are an opportunity to highlight supporting evidence for the claimed disability (ie medical exams, favorable physician opinions, nexus statements).  The focus should be to convince the judge that service connection/higher rating/earlier effective date is justified because there is medical evidence to support it.  Focus on the evidence, the end decision is up to the Board.
All the best.
 

I used to not say this, but after I have been working my claim 15 years, I wished I would have hired an attorney sooner.  Let me explain:
Its above a gs7 pay grade to sign a document which results in 6 figure retro.  Sure, it may happen, but you might win the lottery too.  
Its gonna take a judge to sign that you deserve six figure retro..a regular rating service rep just does not do that.  So, you need to get it to CAVC, or at least BVA asap.  And these guys listen to lawyers..judges are aformer lawyers.  
I suggest you hire an attorney.  OVERCOMING a late filing of any kind is not childs play.  For me, I wont have to pay much for my attorney, if anything at all, because she was already paid 6000 EAJA fees.  This means that VA took a position against me that was "substantially unjustified."   Its what they do.  

Hopefully, someone suggested you file a "substitution of claimant" which is required when the VEteran dies.  
In other words, the claim dies with the VEteran UNLESS you file a substitution of claimant.
There is a time limit for that to happen.  
According to this site, this must happen within a year of the death of the claimant.  
https://blog.eldercounsel.com/does-a-va-pension-claim-die-with-the-claimant
Naturally, if you were represented by an attorney the attorney should have explained this for you.
If represented by a VSO, its hit and miss, more miss than hit.  
If there is a large potential retro, then you should consider legal representation.  I have had a claim in since 2002, and the VA's MO is just like you said...they delay you until you die, then they begin delaying the spouse all over again.  
Since it would appear the severity of your late husband's injuries is not an issue after death, then it boils down to service connection and effective dates.  (for retro). 
Since you have gotten DIC, it sounds like this must have been SC.  Or, your husband passed 10 or more years after he was rated 100% (that is another way to qualify for DIC).  
You may be eligible to file on your late husbands social security.  Check with social security about that.  
Now, on to effective dates, since that may be your primary issue, that is, you are trying to get IU on your deceased hubby.  
YOu want to resubmit those TDIU forms pronto.  Explain those were previously submitted on xx-xx-xxx (date submitted claim for tdiu).  
The effective date for your retro will be the later of "the date filed" or "facts found", which is the date the doc said your hubby became unemployable.  
Check his medical records to see if a doctor said your husband was "unable to maintain SGE" due to his service connected condions.  
You will also need to file the TDIU form on the correct form.  Previously this was not required, but dont take chances here..file it on the correct form, after substitution, of course.  
Unless you are amazingly persistent, organized enough to keep copies of all documents, and great at researching and sorting out case law, you should likely consider an attorney.  
I explain this over and over, but an attorney often costs less than you think, sometimes zero.  Here is why:
When you go to the CAVC and are represented by an attorney, he or she should apply for compensation under EAJA.  The EAJA fees are regurlarly awarded, and that amount will be deducted from any attorney fee you pay.  Example:
I recently went to cavc on an appeal, represented by an attorney, Julie Glover at Glover Luck in DAllas texas.  
My attorney won a remand, and 6000 in attorney's fees.  This means, when/if I do get my retro, the first 30,000 in retro will have no attorney fees.  In other words if my retro is less than 30,000 my attorney fees will be zero.  I will pay 20 percent to any retro ABOVE 30,000.  My attorney charges 20 percent, so 20 percent of 30,000 is 6000.  That is why Im unlikely to pay any attorney fees, and I will be smiling even if I do pay attorney fees, since that would mean I get over 30,000 in retro.  So, if my retro is 35,000:
35,000 times 20% equals 7000
But EAJA paid                -6000
So I would owe 1000 to the attorney and would collect 34,000 in retro.