Based on the provided legal document, the key legal points are as follows:

1. The arbitral tribunal's interpretation of Clause 2.4 (renumbered as 2.8) of the Agreement was found to be erroneous because it sought to restrict the Railway's right to increase the quantity of wagons by up to 30%, which was expressly permitted under the contract (!) (!) .

2. The Tribunal's attempt to re-interpret the contractual clause contrary to its plain language was deemed to amount to re-writing the contract, which is impermissible and conflicts with fundamental principles of contractual enforceability (!) (!) .

3. The Tribunal's decision to award damages based on the difference between the market price and the contract price was considered to be an impermissible re-interpretation of the contractual terms, effectively re-writing the bargain struck between the parties (!) (!) .

4. The Tribunal's conclusion that the Railways' issuance of amendments (notably Amendment No. III) was in breach of the contractual provisions was upheld, but its subsequent award based on the market value and the differential pricing was found to be beyond the scope of the original claims and the contractual rights (!) (!) .

5. The claims related to dual pricing and the alleged breach of the contractual obligation to supply wagons at the agreed price were rejected by the Tribunal, which held that JRIL had not challenged the validity of the contractual provisions permitting the increase in quantity and had accepted the terms (!) (!) .

6. The Court emphasized that interpretation of contractual provisions falls within the jurisdiction of the arbitral tribunal, but an award that seeks to alter or re-interpret clear contractual language to achieve a different outcome is beyond its permissible scope and constitutes patent illegality (!) (!) .

7. The award was ultimately set aside because it was based on re-interpretation of the contract and was inconsistent with the fundamental principles of contractual certainty and legality, amounting to an illegitimate rewriting of the parties' bargain (!) (!) .

8. The Court reaffirmed that commercial contracts are to be interpreted based on their plain language and the intentions of the parties, without judicial or arbitral re-writing of terms to suit perceived commercial difficulties or hardships faced during performance (!) (!) .

In summary, the core legal principles derived from this case highlight that arbitral tribunals must adhere strictly to the clear language of contractual provisions and should avoid re-writing or re-interpreting terms in a manner that alters the fundamental bargain between the parties. Awards based on such re-interpretations are liable to be set aside for patent illegality and conflict with the principles of contractual enforceability.