Mere registering a deed makes it valid?

What you are actually challenging?  The Registration of the deed or the contents of the deed?

When YOU are challenging the authenticity of a registered deed of 25 yrs old it is YOUR burden to prove your contention.

Dear Horn

Registration of sale deed is valid in the eye of law and it is a good piece of evidence of ownership.

it is not clear from your words that wat u challenging whether registration process or content of the deed.

However you have right to challenge both to make it use less. But burden of proof so lies upon u.

Can a decree of partition of a partnership property, having attained finality over an year ago in the absence of any appeal thereagainst, be made a matter of suit for declaration of such Decree to be null and void by any non-joinder to the earlier proceedings before another civil judge ?

You question is not very clear, but as far as I understand about your requirement is that you wants to go in appeal against partition decree by fact that you were not implead as necessary party to the suit. If this is the issue then appeal is barred by limitation act and you can't file a suit related to same subject matter as Resjudicata applies to this.

Mr.Singhal,U can file an appeal with condone delay petition,and a petition to setaside the decree  along wit hdelay petition,setaside petition has to be files within 30days from the date of decree or date of knowledge as u r  effected by the decree and also seek stay of operation of Judgment and decree.No need to file a seperate suit