Sec. 319 crpc

Signatory of the cheque is also liable even if the proprietor is not made party.

Similarly powers u/s 319 are vide and any body can be added as party.

ON BOTH COUNTS THERE ARE NO OF RECENT CITATIONS OF VARIOUS HC S AND EVEN APEX COURT.

YES IT IS POSSIBLE.

In case of proprietorship firm there cannot be two natural accused (more than 1), simply because S.141 is not applicable on proprietorship firm. 

Now the point is the mandate holder, can be an employee, or a relative, or even two joint signatories with authority from proprietor, these people cannot be made accused as per reasons above and also account is of proprietor not of these people. 

Coming to the second question, in CPC, there is a provision, that if plaintiff  makes mistake (or ignorant) about constitution of the respondent firm, then it is on respondent to come forward and state the exact nature. But in criminal under S.138 the offense is not when cheque dishonors, but it is when notice is given and no payment made. So I am sure complainant will not be able to prove that real proprietor indeed received the notice. If the prop firm is also made accused (which itself is non maintainable) then it can be argued by applicant in his favor. Yes, power with the court is there to add, but since NI Act is special act, you never know how the court would decide. One thing is sure mandate holder cannot be convicted, but prop can be added or not at this stage, doubtful. 

Another aspect trial is at decision stage, you stated court was about to acquit, so is this sole ground for acquittal, if the case is getting decided in favor of drawer on merit, then should not be a problem.

The complaint u/s 138 NI Act are governed by Cr. PC (where NI Act is silent on procedural point) the complaint cannot be amended to implicate the original proprietor as additional accused.

The interesting issues come to the light in the court. Suppose court admits the application under S.319 then what about mandate holder? Will it add or substitute the accused? Accused cannot be substituted and in case of prop firms there cannot be two accused under S.141, so prop cannot be added. If the court decides to accept application under S.319, the mandate holder can ask for decision under S.255 CrPC as his trial is over (you said decision stage) and the case cannot move under the existing cause title with a new accused. You can argue that evidence was alleged against mandate holder, and it is not the IPC offense so the state has no role under S.319. A person under NI Act can only be made accused after adopting due procedure like giving notice etc under S.138/139 of NI Act, he cannot be made accused by moving an application under S.319 CrPC. To that extent Dr. Vashista's argument is very sound.

Agree with Roy and Laxminarayan.

Other opinions are bases on bookish knowledge only.

The latest 2013 case law says that =

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There is no dispute with respect to company being accused, once the company stands arraigned, all the responsible people can be brought in with due allegations that too in complaint, but the stated case is of proprietorship firm where there are hundreds of case laws that S.141 is not applicable.  Adv Roy, with due respect, has made a general statement with respect to S.319 CrPC, possibly missed to connect the same with challenges put forth by NI Act.

The order of  Hon SC in "Raghu Lakshminarayanan vs M/S. Fine Tubes on 5 April, 2007" will remove certain cobwebs from the minds of such burning and jumping guns.

There is no need for someone to poke his nose or shove his hand, when it is bound to get burnt, such people should stick to advertising their profession loudly against the ethics. Like those Desi quacks on roadside crossings, they also end up getting many harassed patients and some do get treated out of shear luck but lack of so called bookish knowledge kills many such patients.

iN THIS CONTROVERSIAL CASE SOME SALIENT POINTS ARE TO BE LOOKED INTO, THOSE ARE NAMELY,-

1. Upon whom the demand notice was served , i.e., who is the debtor ?

2. Who is the account holder of the alleged cheque which was returned by the banker ?

3. Who is the signatory of the returned cheque ?

4. What was the remark of the banker for their non-acceptance ?.

5.. What was the mode of receipt of the cheque, by courier, by post or by hand ?

6.  Whether intimation of return of the cheque was made to the account holder ? If yes to whom it was communicated?

On receipt of the abovestated informations I can advise you furthur.