Created a severity custom field for maniphest with below json:

"mycompany:company-severity": {

"name": "Severity",
"type": "select",
"required": true,
"options": {
  "mycompany:critical": "Critical",
  "mycompany:high": "High",
  "mycompany:medium": "Medium",
  "mycompany:low": "Low"
}

Added few tasks with in the system by setting appropriate values for this field. Realized that the "search" key was not set and changed the custom field configuration and added the missing "search" key, now the json looks like below:

"mycompany:company-severity": {

"name": "Severity",
"type": "select",
"required": true,
"search": true,
"options": {
  "mycompany:critical": "Critical",
  "mycompany:high": "High",
  "mycompany:medium": "Medium",
  "mycompany:low": "Low"
}

Though "Severity" field is seen in the Maniphest search page, the tasks created before the "search" key was set are not showing in the search results. How do I get the older ones in the search results ?